//海伦公式
//边abc，半周长d
//s=根号下d*(d-a)(d-b)(d-c)
#include<iostream>
#include<cmath>
using namespace std;
int main()
{
  double x1,y1,x2,y2,x3,y3;
  cin>>x1>>y1>>x2>>y2>>x3>>y3;
  cout.precision(2);
  cout<<fixed;
  double a=hypot(x1-x2,y1-y2);
  double b=hypot(x1-x3,y1-y3);
  double c=hypot(x3-x2,y3-y2);
  double d=(a+b+c)/2;
  cout<<sqrt(d*(d-a)*(d-b)*(d-c));
}
